KR0144640B1 - Liquid indium sources - Google Patents

Abstract

A process for providing medium gaseous trimethyl indium comprising dissolving trimethylindium in a C ₃ -C ₅ trialkylindium solvent to obtain a solution and entraining trimethyl indium from the solution in a carrier gas.

Description

Liquid indium source

1 is a schematic of an apparatus used to deliver vaporized trimethyl indium of the following examples.

2 is a graph showing the number of g of trimethyl indium delivered charged charged versus the delivery time of the following examples.

The present invention relates to a method for providing a uniform radiometric method of vapor phase trimethyl indium in a lamination growth process such as organometallic chemical vapor deposition (MOCVD).

The indium compound most commonly used for MOCVD or other deposition precipitation processes is trimethyl indium. Examples of materials produced by stack growth using trimethyl indium as the indium source are InP, InGaAs, InGaAlP, InGaAsP, InGaAs / GaAs / AlGaAs, InAs, InSb and InAsBi.

A well known disadvantage of using trimethyl indium as the source of indium is the fact that it is a solid at room temperature. A liquid source of organometallic vapor is more preferred than a solid source, because a gas stream of organometallic vapor with an almost constant partial pressure can only be produced by bubbling a carrier gas through the liquid at a constant rate. On the other hand, in the case of using solids, the surface area continues to change as the organic metal source evaporates. In addition, solids, such as trimethyl indium, tend to recondense on the surface of the gas passages, which adds difficulty in providing an even partial pressure of the organometallic compound.

Trimethyl indium as a solid is exceptional compared to other trialkyl indium ie C ₂ -C ₅ alkyl indium being liquid at room temperature. This exception may be because trimethyl indium is present as a tetramer at room temperature, while other trialkyl indium are monomers. However, considering that a sufficiently high vapor pressure should be provided when used for stack growth, it is better to use trimethyl indium with a relatively high vapor pressure.

Several approaches have been attempted to eliminate the complexity due to non-uniform mass flow when using trimethyl indium. Some of these approaches include backflowing the carrier gas through a bubbler; Filling trimethyl indium in an inert material such as Tefion beads in a bubbler; Using two or more trimethyl indium bubblers in succession; And using a solution trimethyl indium in which trimethyl indium is dissolved and / or suspended in high boiling amines or hydrocarbons.

These approaches, in which trimethyl indium remains solid, reduce but do not eliminate non-uniform mass flow.

Trimethyl indium can be dissolved in amines. Its solubility is low (typically about 20%), requiring a large volume of trimethyl indium source. Since amines form a complex with trimethyl indium, there is an advantage in dissolving the tetramer, but there is a disadvantage in that trimethyl indium is bound. Since the use of lamination growth requires a source having only a small amount of high vapor pressure impurities, a highly purified, especially highly purified amine solvent is used with respect to volatile impurities. Nevertheless, if impurities are present they will react with trimethyl indium to produce more new volatile impurities. In addition, even high melting point amines are, to some extent, entrained in the gas stream, creating an undesirable phenomenon of introducing nitrogen into the material to be produced.

High boiling hydrocarbons rule out this nitrogen problem. However, trimethyl indium is significantly less soluble in hydrocarbons than amines, so trimethyl indium is more dispersed in amines than is dissolved in hydrocarbon media. Because hydrocarbons do not dissolve the tetramers, problems arise with the precipitation of trimethyl indium in the gas pathway. In addition, when amine is used, impurities may react with trimethyl indium to generate volatile impurities.

U.S. Patent No. 4,720,560 approaches a problem of producing ethyldimethyl indium by reversible reaction by mixing 2 mol of trimethyl indium and 1 mol of triethyl indium:

2Me ₃ In + Et ₃ In → 3EtMe ₂ In

The preferred source of indium in this process is ethyldimethyl indium, not trimethyl indium. Since the reaction equilibrium depends on the temperature, such as shifting to a right at lower temperatures, it is desirable to maintain the mixture at or below room temperature, eg at about 10 ° C. If a high vapor pressure is required for the growth of the crystal, such low temperatures will be disadvantageous. Increasing the temperature will shift the equilibrium to the left and produce less ethyldimethyl indium.

In the present invention, the liquid source of indium includes trimethyl indium dissolved in a mixture of C ₃ -C ₅ trialkyl indium or C ₃ -C ₅ trialkyl indium. Gases, such as hydrogen or helium, bubbled through this source entrain the trimethyl indium in monomeric form.

Trimethyl indium is well soluble in high melting point trialkyl indium such as C ₃ -C ₅ trialkyl indium. As with the trimethyl indium / triethyl indium system, it is thought that a reversible reaction occurs when trimethyl indium is introduced into higher trialkylindium:

Me ₃ In + (C ₃ -C ₅ alkyl) ₃ In → Me _X (C ₃ -C ₅ alkyl) _(3-X ) In

The expression x = 1 or 2 above.

Trimethyl indium can then be dissolved in up to 2 moles of 1 mole of C ₃ -C ₅ trialkylindium. For example, 320 g of trimethylindium can be dissolved in 286 g of tributyl indium.

Tripropyl indium may be used as the solvent, but butyl indium (or equivalents thereof) such as tri n-butyl indium (bp 85-86 ° C./0.1 mmHg) and triisobutyl indium (bp 71-72 ° C./0.05 mmHg) Blood mixture of tributyl indium) is more preferred due to its high melting point. The solvent is preferably highly purified (eg; purity of 99.999). The use of trialkyl indium as a solvent for trimethyl indium is less volatile than amines or hydrocarbons that react with trimethyl indium to produce volatile impurities, even when small amounts of impurities are first reacted with higher trialkyl indium to be removed during purification. It has the advantage of producing impurities or volatile impurities. In addition, unlike amines that incorporate nitrogen in the precipitated material, higher trialkyl does not incorporate any elements other than those present in trimethyl indium. Like amine solvents, trialkyl indium solvents mill tetramer trimethyl indium in monomeric form, which is in evaporated form.

Unlike the trimethyl indium / triethyl indium system described in US Pat. No. 4,720,560, the only volatile component is mainly trimethyl indium. In addition, at higher temperatures where a greater vapor pressure of trimethyl indium is obtained, the equilibrium shifts to the left to improve the amount of trimethyl indium useful for entraining the carrier gas. As a result, the bubbler can be maintained at a higher temperature, 17-40 ° C., which is a suitable temperature for the bubbler. As a single volatile component is continuously replenished by the equilibrium of the reaction, the amount of trimethylindium entrained by the carrier gas is very constant over time, showing a rather sharp dip when trimethyl indium is almost depleted. More uniform lamination growth can be achieved by precipitating trimethyl indium in a range of concentrations of trimethyl indium where the mass flow of trimethyl indium is constant.

In order to provide the most constant mass flow of trimethyl indium, it is advantageous to initially provide a solution that is saturated or nearly saturated with trimethyl indium.

Suitable carrier gases include those that do not react with trimethyl indium or trialkyl indium solvents. Hydrogen may also be the preferred carrier gas or other gases such as helium or argon.

EXAMPLE

In order to illustrate the invention, the following experiment was performed. 18 g of trimethyl indium (0.11 mol) was dissolved in 15 g (0.05 mol) of tri n-butyl indium in a stainless steel bubbler in a nitrogen filled glove compartment. NMR yielded a colorless transparent solution which appeared to be a BuMe ₂ In composition. Once the solution begins to sink, further dissolution of trimethyl indium (TMI) is not possible. The density of this solution was about 2 g / mL at room temperature.

The apparatus used to measure the flow pattern of this solution in the above experiment is shown in FIG. Inlet 9 of stainless steel (SS) bubbler (source) 10 containing Bu ₃ In / Me ₃ In solution via line 12 to mass flow regulator 16 via a tank of semiconductor grade N2 ( 14). The outlet 17 of the bubbler 10 was connected via line 18 to the outlet 19 of another stainless steel bubbler (receptor) 20 (the second bubbler 20 is the standard in this experiment). In the opposite direction as a result: from the outlet 17 of the bubbler 10 to the outlet 19 of the bubbler 20). The receiver bubbler 20 was cooled by a coil cooler 22 maintained at -15 ° C to -20 ° C. The inlet 24 of this receiver was connected via line 26 to a dry ice-cooled trap 28 to cool the unstable vapor from the receiver 20. Trap 28 was connected to mineral oil bubbler 30 via line 29 to maintain bypass of the N 2 gas.

Another feature of the device is a three-way valve in line 12 used to vent the space between inlet valves 34a of nitrogen bubbler 10, several valves through the line for assembly (34a). ), (34b), (34c), (34d), (34e) and the vacuum section connected to the line 29 (after this connection is made, the space above the receiver valve 34e and the trap 30 are exhausted). It is to include.

The source bubbler 10 was maintained at about 20 ° C. while passing the carrier gas through it at a rate of 500 SCCM. A high flow rate was chosen as above to deplete the contents of the bubbler 10 in a relatively short time. TMIn was observed to be about 40% saturation of carrier gas. Perhaps this is due to the high flow rate and rather low temperature of the source. By lowering the flow rate and increasing the temperature of the source to 30-40 ° C., the saturation of the carrier gas can easily be increased above 80%.

The amount of trimethyl indium conveyed was monitored by the weight loss in the bubbler of the source. NMR spectra were taken periodically to identify material in the source bubbler and the receptor bubbler. The data showed that only trimethyl indium was carried until the end. This was confirmed by the gradual decrease of the methi peaks in the source bubbler. The receptor contained trimethyl indium, a white solid, as evidenced by its NMR.

Radiation measurement results of trimethyl indium are shown in FIG. The linear relationship existed for up to 110 hours and slowed the transport of TMIn at the end. In this experiment, about 13 g of a total of 15 g TMIn (3.0 g consumed for NMR samples) were moved in a very uniform manner, corresponding to 85% of the original TMIn amount. The movement of TMIn did not drop sharply at this stage and did not show irregular movement patterns. NMR spectra show that n-Bu ₃ In rich solutions have at least 80% less TMIn than the original mixture. These data demonstrate that TMIn can be consistently shifted over extended periods of time at a uniform rate. It is also believed that this uniform migration can be further enhanced by suspending additional TMIn in this solution.

Claims (5)

A method of providing a vaporized trimethyl indium comprising dissolving trimethylindium in a C ₃ -C ₅ trialkylindium solvent to obtain a solution, and entraining trimethyl indium with the carrier gas from the solution. The method of claim 1 wherein the solvent is selected from the group consisting of tri n-butyl indium, triisobutyl indium and mixtures thereof. The method of claim 1 wherein trimethyl indium is dissolved in a molar ratio of at least about 0.05 to said solvent. A solution comprising a C ₃ -C ₅ trialkyl indium solvent and trimethyl indium dissolved therein The solution of claim 4 wherein trimethyl indium is dissolved in a molar ratio of about 0.05 or greater with respect to said solvent.